This invention relates in general to a casting machine and in particular to a method of filling a mold cavity of such a casting machine to produce a cast article. Pressure pouring of the molten metal from a furnace to fill a mold cavity has been used for several decades despite a number of problems. At room temperature, the metal is solid and become fluid when melted with sufficient heat. When the metal becomes a fluid, it can become difficult to manage as it begins to assume fluid dynamic characteristics.
It is known to use a low pressure countergravity casting apparatus to cast molten metal into a mold. One example of such an apparatus is described in U.S. Pat. No. 5,215,141. Basically, in a low pressure countergravity casting apparatus, molten metal is supplied to a machine furnace. The machine furnace includes a supply conduit for introducing a gas under pressure into the machine furnace. As the gas is introduced into the machine furnace, the molten metal in the machine furnace is forced through a submerged feed tube, or evacuation conduit, into the mold. The evacuation conduit is commonly referred to as a stalk tube. The mold receives the molten metal through holes in the bottom of the mold. The molten metal in the mold cooling and hardening produces a cast article. A controller is used to adjust the pressure at which the gas is being introduced into the machine furnace. Thus, it can be seen that the machine furnace, the casting apparatus, and the mold are in fluid communication.
One problem in managing the molten metal has been delivering it to the casting apparatus such that the molten metal does not produce a porous cast article. Pores can be formed in the cast article when the molten metal used to make the cast article encounters xe2x80x9csurface turbulencexe2x80x9d during the filling of the mold. Turbulence can cause encapsulation of air into the molten metal and produce undesirable oxides. The oxides are also produced as an encapsulated skin that can weaken the affected portion of the cast article. Thus, it would be desirable to provide an improved method for filling the mold cavity of the casting machine that reduces the amount of turbulence produced during the casting process.
This invention relates to a method for filling a mold of a casting machine to make a cast article. The method includes providing a molten metal to a casting chamber in fluid communication with the mold, the casting chamber having a supply conduit for introducing a gas into the casting chamber, and the casting chamber having an evacuation conduit for delivering the molten metal from the casting chamber to the mold. The method also includes controlling the filling of the mold during a first time interval by delivering the molten metal from the casting chamber to the mold at a first rate. The method further includes controlling the filling of the mold during a second time interval by delivering the molten metal from the casting chamber to the mold at a second rate. The filling of the mold decelerates from the first rate to the second rate and the second rate does not exceed the first rate.
This invention also pertains to a method for filling a mold to make a cast article. The method includes providing a molten metal to a casting chamber, the casting chamber having a supply conduit for introducing a gas into the casting chamber, and the casting chamber having an evacuation conduit for delivering the molten metal from the casting chamber to the mold. The method also includes providing a transducer and a controller. The method further includes during a first time interval controlling the filling of the mold by introducing the gas into the casting chamber at a first rate, and during a second time interval controlling the filling of the mold by introducing the gas into the casting chamber at a second rate. The transducer sends a signal representative of the pressure in the casting chamber and the controller changes the filling of the mold from the first rate to the second rate.
This invention also pertains to a method for filling a mold to make a cast article. The method includes providing a molten metal to a casting chamber, the casting chamber having a supply conduit for introducing a gas into the casting chamber, and the casting chamber having an evacuation conduit for delivering the molten metal from the casting chamber to the mold. The method also includes providing a desired fill profile for delivering the molten metal from the casting chamber to the mold. The method further includes detecting the pressure in the casting chamber and providing a controller and sending a signal representative of the pressure in the casting chamber to the controller. The method also includes changing the desired fill profile based upon the signal representative of the pressure in the casting chamber.
Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.